Storage of red blood cells (RBCs) is a necessary logistical maneuver to allow a sufficient supply of RBC units for transfusion into patients with a wide variety of underlying pathologies. However, storage of RBCs (for up to 42 days at 4C) is a distinctly unnatural process that results in damage to the stored RBCs such that 25% of transfused RBCs (on average) of each unit are cleared within the first 24 hours after transfusion. In addition to decreasing efficacy, the cleared RBCs have the capacity to induce damage to the recipient through both an iron bolus and also through the induction of inflammatory cytokines. In addition, it has been well documented that there is an accumulation of a variety of degradation products during RBC storage, with the potential to cause toxicity when transfused into patients. Included in these products are a wide variety of eicosanoids (i.e. prostaglandins and leukotrienes), which have the capacity to affect immunity, vascular tone, and coagulation. One of the distinct difficulties in both studying the effects of transfusion and also of managing the blood supply is the issue of donor variability. It has long been appreciated that there is wide variation in RBC storage from donor to donor with regards to post-transfusion survival of RBCs. More recently, we have observed that this variation has a basis in underlying metabolic pathways in humans (as studied in project 1 of this application). In the current application, we have applied a tractable mouse model to this issue, and have observed that in mice (as in humans), there is substantial variability in RBC storage from genetically distinct donors. Our preliminary data demonstrate that B6 and FVB mice have profound differences in RBC storage with regards to post-transfusion survival of RBCs and generation of eicosanoids. Moreover, in parallel to human studies (see project 1), FVB RBCs have significantly higher levels of cytidine than do B6 RBCs. In this application, we propose a genome wide association study (GWAS) to elucidate the genetic elements responsible for differential storage. We also propose to go past association, to test causality, through congenic breeding of identified elements. In this context, the grant proposes two specific aims. Specific Aim 1: Identify genetic correlates of RBC storage biology and metabolism. Specific Aim 2: Investigate the causal role of candidate genes in RBC lifespan and storage biology.